Modification and improvement to dynamic bof control

ABSTRACT

A method is disclosed for dynamically controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas to provide a desired final carbon level utilizing instantaneous values of carbon-oxidation rate to determine the end of the blow.

United States Patent Matteson et al.

[ Dec. 18, 1973 MODIFICATION AND IMPROVEMENT TO DYNAMIC BOF CONTROLInventors: Lucius G. Matteson, Pittsburgh;

Norman R. Carlson, Export, both of Pa. 1 Assignees Westinghouse ElectricCorporation,

Pittsburgh, Pa.

Filed: Apr. 5, 1972 Appl. No.: 241,416

Related US. Application Data Continuation of Ser. No. 855,596, Sept. 5,1969, abandoned.

US. Cl. 75/60, 75/59 Int. Cl. C2lc 5/30 Field of Search '75/59, 60

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-Peter D.Rosenberg Att0rrzey-F. H. Henson et al.

[57] ABSTRACT A method is disclosed for dynamically controlling therefining of a bath of iron of known weight by blowing it with oxygencontaining gas to provide a desired final carbon level utilizinginstantaneous values of carbonoxidation rate to determine the end of theblow.

13 Claims, 4 Drawing Figures CONTROLS FOR .1

OXYGEN FLOW DISPLAY OXYGEN LANCE 3,? 140 AND COOLANT ADDITION DIGITALCOMPUTER SYSTEM T 22\ J34 OXYGEN FLOW, PRESSUREJEMPERATURE,

CHARGE WEIGHT, BATH BLOWING CONDITIONS, GAs TEMPERATURE TARGETHNALTEMP." FLOW DETECTOR AND C (FeO) etc. L

ACTUAL CONDITIONS FROM 32 PREVIOUS HEATS 25 23 30 {3 r r as C02 H20 0 coBASIC OXYGEN FURNACE MODIFICATION AND IMPROVEMENT TO DYNAMIC BOF CONTROLThis is a continuation, of application Ser. No. 855,596 filed Sept. 5,1969.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to steel-making processes and more particularly to improvedmethods for dynamic control of the carbon content and temperature of thesteel bath in a top blown oxygen steelmaking converter such as the basicoxygen furnace (BOF).

2. Description of the Prior Art It may be explained that in the basicoxygen steelmaking process, a lance is controllably positioned to feed acontrolled amount of oxygen into the basic oxygen vessel principally forthe purpose of heating and decarburizing the metal bath. Since carbonlevel significantly effects the properties of steel product, it isnecessary that the carbon level of steel made in the BOF be controlledas in the case of other types of steelmaking furnaces and further thatthe carbon control be compatible with other BOF controls such asendpoint temperature control placed on the bath. By the term carbonlevel, it is meant herein to refer to the weight percentage of carbon ina quantity of steel. By the term carbon content, it is meant herein torefer to the weight of carbon in a quantity of steel. When the weight ofa quantity of steel is known, the carbon content can readily bedetermined from the carbon level and vice versa.

In commercial practice, it is desirable that carbon level andtemperature control be effective during the BOP steelmaking process toproduce specified carbon level steel at the desired temperature at theprocess endpoint. By the terminology process endpoint, it is hereinintended to refer to a point in time just prior to vessel turndownusually about 25 to 30 minutes after oxygen blowing begins.

Various methods have been developed in an attempt to effect carbon leveland temperature control during the BOP steelmaking process. One recentlydeveloped process is disclosed in US. Pat. No. 3,377,158 entitledConverter Control Systems and Methods. As the present invention is animprovement of the methods disclosed in that patent, said patent ishereby incorporated by reference herein.

Briefly and with reference to FIG. 3 of the drawings, the method ofcontrol disclosed in said patent generally involves determination,preferably by a computer, of values of carbon-oxidation rate d) for theheat being controlled through the flat portion of the illustrateddecarburization rate versus carbon level curve. There is a basicassumption that at low levels of remaining bath carbon there is anexponential relationship between the value of carbon-oxidation rate, ascalculated by a computer, and the remaining bath carbon content. Thecarhon-oxidation rate continues to be determined into the dynamicfall-off region of the curve until the instantaneous value ofcarbon-oxidation rate descends to approximately eight or nine tenths ofthe value of the horizontal asymptote, i.e., at point t,

The computer then uses determined carbonoxidation rate values andcurve-fitting techniques to project a carbon endpoint curve, that is theremaining end portion of the carbon-oxidation rate curve. The computerthen calculates from the projected curve end portion the amount ofadditional oxygen needed to reduce the present bath carbon level to thedesired endpoint or target value C Next the computer predictivelycalculates the increase in bath temperature that will result fromblowing the amount of oxygen predicted for reducing the carbon level tothe target value C At this time, the bath temperature is recorded by animmersion thermocouple and this temperature plus the rise in temperaturepredicted from the additional oxygen to be blown is the predicted bathendpoint temperature when endpoint carbon C is reached. if thisprojected endpoint temperature is acceptable the blow continues asscheduled; if, however, the predicted endpoint temperature isoff-target, the computer recommends corrective actions. If, for example,the molten steel is expected to be colder than desired when the endpointcarbon content is reached, the computer advises blowing additionaloxygen to generate additional heat, and it calculates the quantity ofadditional oxygen needed to reach target temperature. If, on the otherhand, the predicted endpoint temperature at endpoint carbon C is toohigh, the computer calculates not only the additional amount of oxygenrequired to reduce the endpoint carbon level to C, but also the amountof coolant needed to reduce the temperature to the target temperature.The coolant, usually limestone, is added to the BOP during the remainderof the blow.

The dynamic control method just described estimates oxygen volume toblow down to the target carbon C from an estimate of current carbonlevel in the bath which is made at a relatively high carbonoxidationrate value, i.e., at 1,. The accuracy with which the endpoint carbonlevel can be controlled is accordingly materially limited by the extentto which the actual end portion of the carbon-oxidation rate curvedeviates from the end curve portion predicted from the relatively highcarhon-oxidation rate value.

SUMMARY OF THE INVENTION The present invention provides a method ofcontrolling the refining of a bath of iron of known weight by blowing itwith oxygen containing gas comprising the steps of determining thecontent of carbon and oxygen compounds in the waste gases per unit oftime throughout the blow and flow of waste gases, determining the amountof oxygen blown per unit of time throughout the blow, determining fromthe preceding two determinations successive values of carbon-oxidationrate over a predetermined portion of the blow after carbonoxidation ratefall-off, determining successive values of bath carbon level from thesuccessive values of carbonoxidation rate, and terminating the blow ofoxygen containing gas at the point in time at which it is determinedfrom the carbon-oxidation rate values that the carbon level of the bathhas fallen to the desired value unless predetermined conditions directotherwise.

Preferably, the final temperature may be fixed by making a temperaturereading of the bath at a preselected point in the blow, calculating thebath endpoint temperature on the basis of the temperature reading andthe carbon level in the bath as the carbon level is determined, and whenrequired, adjusting the point of termination of the blow and supplying acoolant to control the endpoint temperature to the desired level, saidcoolant preferably being free of material that would otherwise supplycarbon to the bath.

The present invention, therefore, provides a method utilizing successivevalues of carbon-oxidation rate to determine successively betterpredictions for the end of the oxygen blow. Practice of the inventiontightens the limits within which carbon level can be controlled in anaccurate and efficient manner which is compatible with other BOF processcontrols such as endpoint temperature control placed on the bath.

BRIEF DESCRIPTION OF THE DRAWINGS A complete understanding of theinvention may be obtained from the foregoing and the followingdescription thereof, taken together with the appended drawings, inwhich:

FIG. 1 shows a basic oxygen furnace with an oxygen lance;

FIG. 2 shows BOF control apparatus for carrying out the invention;

FIG. 3 shows a curve of decarburization rate versus carbon; and

FIG. 4 shows a curve of carbon oxidation rate versus carbon level,illustrating the diminishing effect of 4; value noise on carbon level asthe carbon level diminishes.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawingswherein like reference numerals refer to like parts throughout theseveral views, there is illustrated in FIG. 1 a basic oxygen furnace ofconventional design provided with a hood l2, ducting 14 leading tostacks (not shown), a vertically movable lance l6 and a coolant supplyhopper 18. As shown in FIG. 2, a gas flow meter is provided, usually onthe stacks, to determine by measurement the rate of waste gas flow. Thisrate is fed by line 22 to a programmed digital computer system 24. Gasanalyzers 26, 28, 30 and 31 are used for determining the C0, C0 H 0 and0 content of the waste gases. The results of the analysis are fed to thecomputer 24.

A bath temperature or a continuous series of bath temperature readingscan be made by a bath temperature detector 32. The detector 32 may, forexample, be a device known in the trade as a bomb thermocouple when onlyone temperature reading is to be made or it can be a sheathed protectedthermocouple when a series of temperature readings are to be made.Readings from the detector 32 are fed by line 34 to the computer 24.

Conventional instrumentation shown as block 36 is provided forautomatically determining and feeding to the computer 24 the oxygen flowrate, pressure and temperature and for manually or automatically feedingthe determined blowing conditions such as target temperature and targetcarbon. The computer 24 is programmed to supply the final data todisplay and printout iinstruments as indicated at 38 and 40,respectively. If desired, coolant source controls and oxygen lancepositioning controls and oxygen flow controls can be computer operatedas indicated by the reference character 41. Those skilled in the artwill understand that the apparatus thus far described is conventional.

A brief outline of the manner heretofore utilized in operating suchequipment will aid in the understanding of the present invention and themanner in which the present invention, departs from the prior art, andmore specifically the manner in which the invention departs from theabove-mentioned U.S. patent.

Outline of Prior Art Practice The required data generated in real timefor the heat which it is desired to control and which is fed ,to thecomputer is essentially that data required to calculate thecarbon-oxidation rate In order to calculate the carbon-oxidation rate(11 measurements are made of (l) the content of carbon and oxygencompounds in the waste gas for a given period of time and (2) the amountof oxygen blown during the same period of time. By dividing the measuredcarbon content of the waste gas per unit of time by the amount of oxygenblown per unit of time, the carbon-oxidation rate 4) is determined. Asis known, the functional relationship between the carbon-oxidation rated) and the carbon content of the bath is as shown in Equation (1):

where:

4) is the carbon-oxidation rate in points carbon /1 ,000

SCF of oxygen;

0:, B and 'y are parameters; and

C is the carbon level in the bath.

The graph shown in FIG. 3 is a typical example of a member of a familyof curves of carbon-oxidation rate to carbon level of the bath for afurnace. The parameters a, B and 'y have unique values for anyparticular curve. To implement computer control it is necessary todetermine which carbon-oxidation carbon content curve is being followedduring the progress of refining. Once this is done, a measured value ofda can then be used by the computer to calculate a corresponding valuefor C and the volume of oxygen to move from the calculated carbon levelto the desired endpoint carbon level.

A number of techniques have been developed to forecast, in real time,values of a B and y for the heat under control. Briefly, one techniquerelies on the facts that the decarburization curve intercepts the carbonaxis at a relatively fixed value, and that a the asymptotic value of thecurve, can be determined during actual refining. The value of thevariable 'y can then be determined at time t from the ratio of the firstderivative to the second derivative of the equation of the curve. Thisbriefly outlined technique is more fully set forth in theabove-mentioned U.S. patent.

Having determined at I, the values of a B and y for the heat it isdesired to control, the computer uses Equation (1) and measured (b at t,to calculate C at 1,. Integrating the relation between bath carbon andcarhon-oxidation rate (Equation 1) over the limits from the determinedvalue of bath carbon level at t, to the desired final value (C producesthe volume of oxygen which must be blown in order to arrive at thedesired final carbon concentration. Under prior art practice, thisvolume of oxygen is then blown unless temperature corrective controlaction is required.

The dynamic control method just described is commercially effective butit is characterized with deficiencies including the following:

I. The single determination at time t, of the carbonoxidation curve (forthe heat it is desired to control) is inaccurate, because not enough ofthe fall-off portion of the curve has been observed, with the resultthat determination of the parameter at I, is imprecise. From Equation (1it is evident that imprecision in 'y generally causes imprecision in thecalculation of C from measured d) and in particular this is so at timet,. Equation (2) illustrates the error in C at t, which is causedby anerror in estimating at z,

where:

A C is the error in carbon level in weight percent; A y is the error inestimating the true value of y y is the true value of 'y for heat beingfollowed; a is the true value of a for heat being followed; and 4) I isthe value of d) at t, Since 4) at t is approximately 0.85 a and yat-this point typically is approximately 4.5, it follows that:

A C/A 'y l/(4.5) ln(0.l5) l.9/20.25 0.0938

Thus, a percent error in 'y (A 'y 0.45) causes an error in C of 0.042weight percent at time t,

2. Having determined the values of 'y and C at time t the describedmethod thereupon proceeds to estimate the volume of oxygen necessary tomove from the carbon level at t, to the target level C Inaccuracy indetermining 'y at t also affects the estimate of oxygen volume requiredto reach C as shown by Equation (3):

the symbol A preceding a character indicates the error in estimating itsvalue and those characters not preceded by the A symbol are true valuesfor the heat being followed;

C is the intercept of the carbon-oxidation rate curve with the carbonlevel axis.

A set of typical values which are seen in daily operation of the BOPprocess are as follows:

Substituting these values in Equation (3) gives the following:

Am/A 10 101728 17, 230.

' any), no utilization is made of (11 values which occur between t andendpoint. Thus, the method ignores those 4) values which otherwise wouldcontribute to more accurate estimates of the y parameter as well as moreprecise determinations of current bath carbon level. Greater precisionin the determinations of current bath carbon level result from the factthat d) noise causes less carbon estimation inaccuracy as carbon leveldecreases as is illustrated in FIG. 4. It can be seen from FIG. 4, thatwith incertainty in d) determinations caused by noise, bath carbonlevels are more accurately calculated as the bath carbon leveldiminishes.

4. Utilization of any carbon-bearing coolant such as limestone duringthe blow affects the measured values, thereby rendering them useless forindicating more accurately the carbon-oxidation curve for the currentheat or for indicating the current bath carbon level. In this sense themethod is self-defeating, as it destroys the very information whichotherwise would improve the control of target carbon level andtemperature.

DESCRIPTION OF THE METHOD IN ACCORDANCE WITH THE INVENTION In thepresent invention the computer 24 is programmed to calculate d) valuesfrom process measurements in the manner previously described. Morebeneficially, however, calculation and storage of (b is performed at theend of each of successive data sampling intervals, preferably every 5seconds through the blow. At time t,, the 'y parameter is estimated (thea parameter is determined by averaging values of (I) previously observedfor the heat it is desired to control, and the B parameter isestablished by the fixed intercept of the d) curve with the carbonaxis). Having made an initial estimate of 'y the computer estimates thevolume of oxy' gen to endpoint, and the temperature at endpoint, andrecommends an amount, perhaps zero, of substantially non-carbon-bearingcoolant such as scrap or iron ore.

Because non-carbon-bearing coolant is used, values of (b which arecalculated after 2, and preferably throughout the remaining part of theblow period, continue to provide valid process information particularlyregarding -y and bath carbon level. Each new value of d) after time t isused in conjunction with those already recorded to provide anincreasingly more precise determination of 'y and thus an increasinglymore precise indication of bath carbon level. Thus, it is preferred asalready indicated that ii; calculations and carbon level estimations bemade throughout the blow, although such calculations and estimations canbe terminated at a point in time between t and the end of the blow. Ifthe last carbon level estimate occurs between 1 and the end of the blow,the remaining oxygen volume calculation associated with the last carbonestimate would ordinarily be used to define the point in time at whichthe blow is ended for predicted attainment of target carbon level.

In order to implement the redetermination of upon receipt of each new qSvalue, let:

(I) t observed value of (b at time 1,;

qb, first observed value of (b one sampling interval after t 4) n nthobserved value of 5 n sampling intervals after t, Then from Equation(1):

11) t a [38 m 4), a Be +pe n. Consider d) t, and 5, where da is thevalue of d: observed m sampling intervals after t but before (1) hence:

In(zbt z, 1 mo:)=-y(C, C,,,). 4

In Equation (4), 1 and (11, are observed by the computer, and a is knownfor the heat it is desired to control by averaging observed values of 5prior to the falloff region of the curve. Equation (4) indicates thateach time a new value of (b is observed, a new updated estimate of -y isavailable provided that the difference in carbon levels (C, C,,,) isknown. Because the computer records waste gas flow and content of carboncompounds (C0, C0 it is therefore programmable to calculate thedifference in bath carbon level between any two points of time bycalculating the amount of carbon removed in the waste gas between thesame two points of time. The computer forms in its memory a table ofobserved d) values and corresponding bath carbon level differences asfollows:

(1) t, no entry An entry is made in this table at the end of eachsampling interval. The computer makes entries until the heat reachesendpoint.

Although each pair of values in the table provides an estimate of'ythrough Equation (4), a more meaningful estimate can be made by means ofthe least squares method, which uses all value pairs from t to the mostrecent entry. Thus, if the most recent entry in the table is the Kth,then 'y is given by Equation (5);

At the end of each sampling period, the computer enters a new pair ofvalues in the table, advancing K by one unit, following which it employsEquation (5) and all value pairs to date (up to and including the Kth)to redetermine y Then the carbon-oxidation curve and the newobservations of da are used to calculate both the current bath carbonlevel and the oxygen volume to target carbon. These values are displayedto operating personnel. When the calculated oxygen volume to targetcarbon reaches zero or when the calculated bath carbon level reaches thetarget value, the oxygen blow is terminated in accordance with thepreferred practice of the invention.

An important feature of the invention is that the carbon-oxidation curveparameter 7 is redetermined at the end of successive sampling intervalsfrom I to a subsequent time point in the blow and preferably to the endof the blow, with the result that each redetermination considers yetanother value in the fall-off portion of the carbon-oxideation curve,yielding estimates of y of ever increasing accuracy, and sharplycontrasting with the prior art practice which estimates 7 only at time2,. Utilization of 11 values, observed in the dynamic fall-off portionof the carbon-oxidation curve after t, for determination of y values ofever increasing accuracy illustrates that the method of the inventionenables computer control of the BOP without reference to past vesselhistory as is the practice of the prior art. Because the current bathcarbon level is estimated at the end of successive sampling intervalsthe estimates become increasingly more accurate due to the increasingaccuracy ofy and due to the lower sensitivity of bath carbon level to (bvalue noise as the carbon level diminishes as pointed out above withreference to H6. 4. Therefore, endpoint chemistry and particularlyendpoint carbon level is made more accurately controllable.

At the end of each sampling interval after time 1,, the newly determinedcarbon-oxidation curve yields a new and more accurate estimate of thetime of the forthcoming end of the blow. Therefore, it is useful anddesirable to display, after each redetermination of 'y for operatingpersonnel not only the current bath carbon level and volume of oxygen totarget, but also the forecast temperature when target carbon level isreached, basing said temperature forecast on a single temperaturemeasurement made at a preselected time (prior to t,), on the coolingeffect of the non-carbon bearing coolant recommended at t,, the size andmakeup of the bath and on the volume of oxygen elapsing between the timeof the preselected temperature measurement and the time of the newlyforecast endpoint. Displays of current carbon level, oxygen volume totarget and temperature at target, are updated each time a new (i) valueis observed after t,, so that operating personnel are cognizant of themost accurate indicators of the state of the metal bath. If a newtemperature prediction based on the current carbon endpoint predictionshows that coolant or added heat is needed to reach the targettemperature, a new temperature corrective action is preferablydetermined by the computer and it is taken during the remaining part ofthe blow or, if desired in the case of a coolant addition action whichtakes about 15 to 20 seconds to perform and about 1 /2 minutes forcoolant dispersion, after the termination of the blow and prior toactual bath temperature measurement after the blow. In many cases,temperature corrective action involving an extended oxygen blow wouldtake precedence over target carbon requirements, i.e., the heat would beaccepted at target temperature with low but correctable carbon level. r

With regard to endpoint temperature control it is also possible inaccordance with the invention to make more than one discrete bathtemperature measurement, or to measure the bath temperaturecontinuously, by means of a sheathed thermocouple, for example. Ineither case, the temperature forecasting for target carbon level isbased on the most recent measurement of bath temperature and on theelapsed oxygen volume between the time of said most recent temperaturemeasurement and the time of the newly predicted carbon endpoint.Accuracy of predicted temperature at target carbon is substantiallyincreased by making temperature measurements at preselected pointsbetween t, and endpoint, as opposed to the single preselected pointbefore It is within the spirit of the invention to measure the bathtemperature endpoint by means of a bombthermocouple, thermocouple lance,or any other temperature measuring device which is capable of measuringbath temperature with the vessel upright. This eliminates the loss ofproduction time involved in rotating the vessel to enable insertion ofthe standard dip-type immersion thermocouple customarily used in theiron and steelmaking industry. It is also within the spirit of theinvention to enter the measured endpoint temperature into the computereither automatically or mechanically, after which the computercalculates additional oxygen if the bath temperature is low, oradditional coolant if the temperature is high. Control of'oxygen orcollant addition may be under operator command or it may be undercomputer control as indicated bythe reference character 41.

It has been determined that practice of the dynamic control method ofthe above-mentioned US. patent has improved the process control in a BOFby more than two to one; that is twice as many heats reach the desiredendpoint temperature and carbon content'without reblowing. By the use ofthe method of the present invention, even higher efficiency andproductivity can be expected since successive instantaneous values ofcarbon-oxidation rate are utilized during the fall off of the carbonoxidation rate to make successive projections of the end of the oxygenblow with increasing accuracy. This contrasts with the prior art methodof estimating the required oxygen volume to blow down to the desiredendpoint carbon level from an estimate of bath carbon which isdetermined from a carbon oxidation rate value made at a relatively earlyprocess time point.

The foregoing description has been presented only to illustrate theprinciples of the invention. Accordingly, it is desired that theinvention not be limited by the embodiment described, but rather, thatit be accorded an interpretation consistent with the scope and spirit ofits broad principles. What is claimed is:

1. A method of controlling the refining of a bath of iron of knownweight by blowing it with oxygen containing gas, said method includingthe steps of:

measuring the content of carbon and oxygen compounds in the waste gasesper unit of time during the blow;

measuring the amount of oxygen blown per unit of time during the blow;

determining from said content of carbon and oxygen compounds and saidamount of oxygen a plurality of successive values of carbon oxidationrate over at least a predetermined period after carbon oxidation ratefall off and substantially up to the termina- 4 tion of the blow;

determining a plurality of successive values of bath carbon leveldifference respectively corresponding to said successive values ofcarbon oxidation rate;

determining from said plurality of carbon oxidation rate values and saidplurality of carbon level difference values at least one value of carbonlevel of said bath; and

controlling the blow of oxygen containing gas to terminate when saidvalue of carbon level of the bath has a predetermined relationship to adesired target carbon level.

2. A method of controlling the refining of a bath of iron of knownweight by blowing it with oxygen containing gas as set forth in claim 1,wherein:

the plurality of successive carbon oxidation rate values are determinedas a sampled data series of values over at least a substantial part ofthe carbon oxidation rate fall off period substantially up to thetermination of the blow;

the plurality of successive carbon level values are determined as asampled data series of values respectively corresponding in relation totime to the carbon oxidation rate values; and

said blow is terminated at a point in time when the carbon level valueof said bath substantially equals a desired target carbon level value.

3. A method of controlling the refining of a bath of iron of knownweight by blowing it with oxygen containing gases set forth in claim 1,wherein said method further includes the steps of:

measuring at least one temperature value of the bath;

determining at least one bath endpoint temperature on the basis of themeasured temperature value and at least one bath carbon level value; and

making any desired temperature corrective action in response to thedetermined bath endpoint temperature before the desired processendpoint.

4. A method of controlling the refining of a bath of iron of knownweight by blowing it with oxygen containing gas as set forth in claim 1wherein said method additionally includes the step of determining atleast one value of oxygen volume required to reach the desired targetcarbon level.

5. A method of controlling the refining of a bath of iron of knownweight by blowing it with oxygen containing gas as set forth in claim 2,wherein said method additionally includes the step of determining arespectively corresponding plurality of oxygen volume values required toreach the desired target carbon level from the determined carbon levelvalues and carbon oxidation rate values.

6. A method of controlling the refining of a bath of iron of knownweight by blowing it with oxygen containing gas as set forth in claim 1,wherein said method further includes the steps of:

measuring the temperature value of the bath at least at one preselectedpoint in the blow;

calculating the bath endpoint temperature on the basis of the measuredtemperature value, and, making at least one bath temperature correctiveaction selected from predetennined actions including adjusting thecarbon determined point of termination of the blow of oxygen containinggas and supplying a coolant substantially free of material that wouldotherwise supply carbon to the bath.

7. A method of controlling the refining of a bath of iron of knownweight by blowing it with oxygen containing gas as set forth in claim 1,wherein said method further includes the steps of:

measuring at least one actual bath temperature during the blow;

calculating the bath endpoint temperature on the basis of said measuredtemperature and thecorresponding bath carbon level value; and

making a desired temperature corrective action in response to said bathendpoint temperature before the process endpoint.

8. A method of controlling the refining of a bath of iron of knownweight by blowing it with oxygen containing gas as set forth in claim 1,wherein said method further includes the steps of:

measuring at least one actual bath temperature during the blow;

calculating the bath endpoint temperature in relation to at least saidone temperature and the corresponding carbon level difference value, andmaking at least one bath temperature corrective action in relation tosaid endpoint temperature and selected from adjusting the carbondetermined point of termination of the blow of oxygen containing gas andsupplying a coolant to the bath.

9. A method of controlling the refining of a bath of iron of knownweight by blowing it with oxygen containing gas as set forth in claim 1,wherein:

the carbon oxidation rate values are determined as a sampled data seriesof values over at least a selected part of the carbon oxidation ratefall off period and substantially up to the termination of the blow;

The carbon level difference values are determined as a sampled dataseries of values respectively corresponding to said rate value series;and

the blow is controlled to terminate when the carbon level of the bathsubstantially equals the desired target carbon level.

10. A method of controlling the refining of a bath of iron of knownweight by blowing it with oxygen containing gas as set forth in claim 1,wherein:

the carbon oxidation rate values are determined as a sampled data seriesof values over at least a selected part of the carbon oxidation ratefall off period and substantially up to the termination of the blow;

the carbon level difference values are determined as a sampled dataseries of values respectively corresponding to the rate value series;and

the blow is controlled in response to said carbon oxidation rate valuesand said carbon level difference values to terminate when the carbonlevel of the LII bath substantially equals the target carbon level.

11. A method of controlling the refining of a bath of iron of knownweight by blowing it with oxygen containing gas as set forth in claim 1,wherein:

the carbon oxidation rate values are used to make successively moreaccurate approximations of the carbon oxidation rate versus carboncontent curve defined by the equation d) a B e 7 where d) is the carbonoxidation rate, a is the curve asymptote value, C is the bath carboncontent, and y and B are unknown parameters and the successive curveapproximations include determining a series of updated valuesrespectively corresponding to the series of carbon oxidation ratevalues.

12. A method of controlling the refining of a bath of iron of knownweight by blowing it with oxygen containing gas as set forth in claim1], wherein the updated values of 7 are derived from equation:

4),, carbon oxidation rate value at time a.

d) 5 carbon oxidation rate value at later time n.

C carbon level value at time a.

C, carbon level value at later time n.

13. A method of controlling the refining of a bath of iron of knownweight by blowing it with oxygen containing gas as set forth in claim11, wherein each updated value ofy is a weighted combination of thepresent and all previous 7 values determined for the same heat with theuse of the said equation.

2. A method of controlling the refining of a bath of iron of knownweight by blowing it with oxygen containing gas as set forth in claim 1,wherein: the plurality of successive carbon oxidation rate values aredetermined as a sampled data series of values over at least asubstantial part of the carbon oxidation rate fall off periodsubstantially up to the termination of the blow; the plurality ofsuccessive carbon level values are determined as a sampled data seriesof values respectively corresponding in relation to time to the carbonoxidation rate values; and said blow is terminated at a point in timewhen the carbon level value of said bath substantially equals a desiredtarget carbon level value.
 3. A method of controlling the refining of abath of iron of known weight by blowing it with oxygen containing gasessEt forth in claim 1, wherein said method further includes the steps of:measuring at least one temperature value of the bath; determining atleast one bath endpoint temperature on the basis of the measuredtemperature value and at least one bath carbon level value; and makingany desired temperature corrective action in response to the determinedbath endpoint temperature before the desired process endpoint.
 4. Amethod of controlling the refining of a bath of iron of known weight byblowing it with oxygen containing gas as set forth in claim 1 whereinsaid method additionally includes the step of determining at least onevalue of oxygen volume required to reach the desired target carbonlevel.
 5. A method of controlling the refining of a bath of iron ofknown weight by blowing it with oxygen containing gas as set forth inclaim 2, wherein said method additionally includes the step ofdetermining a respectively corresponding plurality of oxygen volumevalues required to reach the desired target carbon level from thedetermined carbon level values and carbon oxidation rate values.
 6. Amethod of controlling the refining of a bath of iron of known weight byblowing it with oxygen containing gas as set forth in claim 1, whereinsaid method further includes the steps of: measuring the temperaturevalue of the bath at least at one preselected point in the blow;calculating the bath endpoint temperature on the basis of the measuredtemperature value, and, making at least one bath temperature correctiveaction selected from predetermined actions including adjusting thecarbon determined point of termination of the blow of oxygen containinggas and supplying a coolant substantially free of material that wouldotherwise supply carbon to the bath.
 7. A method of controlling therefining of a bath of iron of known weight by blowing it with oxygencontaining gas as set forth in claim 1, wherein said method furtherincludes the steps of: measuring at least one actual bath temperatureduring the blow; calculating the bath endpoint temperature on the basisof said measured temperature and the corresponding bath carbon levelvalue; and making a desired temperature corrective action in response tosaid bath endpoint temperature before the process endpoint.
 8. A methodof controlling the refining of a bath of iron of known weight by blowingit with oxygen containing gas as set forth in claim 1, wherein saidmethod further includes the steps of: measuring at least one actual bathtemperature during the blow; calculating the bath endpoint temperaturein relation to at least said one temperature and the correspondingcarbon level difference value, and making at least one bath temperaturecorrective action in relation to said endpoint temperature and selectedfrom adjusting the carbon determined point of termination of the blow ofoxygen containing gas and supplying a coolant to the bath.
 9. A methodof controlling the refining of a bath of iron of known weight by blowingit with oxygen containing gas as set forth in claim 1, wherein: thecarbon oxidation rate values are determined as a sampled data series ofvalues over at least a selected part of the carbon oxidation rate falloff period and substantially up to the termination of the blow; Thecarbon level difference values are determined as a sampled data seriesof values respectively corresponding to said rate value series; and theblow is controlled to terminate when the carbon level of the bathsubstantially equals the desired target carbon level.
 10. A method ofcontrolling the refining of a bath of iron of known weight by blowing itwith oxygen containing gas as set forth in claim 1, wherein: the carbonoxidation rate values are determined as a sampled data series of valuesover at least a selected part of the carbon oxidation rate fall offperiod and substantially up to the termination of the blow; the carbonlevel differencE values are determined as a sampled data series ofvalues respectively corresponding to the rate value series; and the blowis controlled in response to said carbon oxidation rate values and saidcarbon level difference values to terminate when the carbon level of thebath substantially equals the target carbon level.
 11. A method ofcontrolling the refining of a bath of iron of known weight by blowing itwith oxygen containing gas as set forth in claim 1, wherein: the carbonoxidation rate values are used to make successively more accurateapproximations of the carbon oxidation rate versus carbon content curvedefined by the equation phi Alpha + Beta e C, where phi is the carbonoxidation rate, Alpha is the curve asymptote value, C is the bath carboncontent, and gamma and Beta are unknown parameters and the successivecurve approximations include determining a series of updated valuesrespectively corresponding to the series of carbon oxidation ratevalues.
 12. A method of controlling the refining of a bath of iron ofknown weight by blowing it with oxygen containing gas as set forth inclaim 11, wherein the updated values of gamma are derived from equation:ln ( phi a - Alpha )/ phi n - Alpha -> gamma (Ca - Cn) where: phi acarbon oxidation rate value at time a. phi n carbon oxidation rate valueat later time n. Ca carbon level value at time a. Cn carbon level valueat later time n.
 13. A method of controlling the refining of a bath ofiron of known weight by blowing it with oxygen containing gas as setforth in claim 11, wherein each updated value of gamma is a weightedcombination of the present and all previous gamma values determined forthe same heat with the use of the said equation.